1. Field of the Invention
This invention relates to a wire dot printer in which wires are selectively projected by a plurality of electromagnets to effect printing (including recording).
2. Description of the Prior Art
When it is desired to form a character by a dot matrix, if it is assumed that an m.times.n dot matrix is disposed as shown in FIG. 1 of the accompanying drawings, use is made of a printing head comprising n wires arranged in a row at a pitch P.sub.2 in the longitudinal direction and, if this printing head is shifted to right or left m times at a pitch P.sub.1 and the wires are designed so as to be capable of being driven for each pitch, there can be formed m.times.n dot matrices.
Generally, a wire dot head is such that an armature is attracted and operated by an electromagnet contained in the head body and a wire is urged against printing paper by the armature through an ink ribbon, whereby desired printing is effected by the aforementioned dot matrices. When the armature is attracted and operated, heat is generated by excitation of the coil of the electromagnet and therefore, the head body heats. Accordingly, exciting current is decreased by the increase in coil resistance caused by this heating and the force which electromagnetically attracts the armature is reduced and the operation efficiency of the armature is reduced. Therefore, the urging drive force, i.e., the printing pressure, of the wire connected to the armature becomes small, thus resulting in a reduced quality of printing. Also, the surface temperature of the head rises to the order of 90.degree. C., and this is very dangerous to the operator.
Also, a wire dot printer effects printing by impact and this leads to the advantage that several copies can be produced at a time, but as a disadvantage thereof, noise is great. Accordingly, such noise has limited the use of conventional wire dot printers in offices. There are two causes of the sound produced when printing is effected by the use of such a wire dot printer. A first cause is the impact sound produced when dots are printed on printing paper. The quality of such impact sound is determined by the material and hardness of the platen, the mounted condition of the printing paper and the printing force of the wire. A second cause is the stop sound produced when the armature to which the wire is connected is stopped by a stopper in the course of its return to the original position after completion of printing.
In the wire dot printer, not only noise produced by such collision of the wire, but also the operation of the armature becomes unstable due to the creation of rebound of the armature, and this has led to the shortcoming that the quality of printing is deteriorated.
Thus, the conventional wire dot printers have not always been sufficient in the operation efficiency of the armature.